CVE-2026-63942 parport: Fix race between port and client registration
A race condition in the Linux kernel parport subsystem allows client drivers to attach to uninitialized ports, potentially causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63942?
CVE-2026-63942 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
parport: Fix race between port and client registration
The parport subsystem registers port devices before they are fully initialised, resulting in a race condition where client drivers such as lp can attach to ports that are not completely initialised or even being torn down.
When the port and client drivers are built as modules and loaded around the same time during boot, this occasionally results in a crash. I was able to make this happen reliably in a VM with a PC-style parallel port by patching parport_pc to fail probing:
> --- a/drivers/parport/parport_pc.c > +++ b/drivers/parport/parport_pc.c > @@ -2069,7 +2069,7 @@ static struct parport *__parport_pc_probe_port(unsigned long int base, > if (!p) > goto out3; > > - base_res = request_region(base, 3, p->name); > + base_res = NULL; > if (!base_res) > goto out4; >
and then running:
while true; do modprobe lp & modprobe parport_pc wait rmmod lp parport_pc done
for a few seconds.
In the long term I think port registration should be changed to put the call to device_add() inside parport_announce_port(), but since the latter currently cannot fail this will require changing all port drivers.
For now, add a flag to indicate whether a port has been "announced" and only try to attach client drivers to ports when the flag is set.
Weakness: CWE-362
Which versions are affected by CVE-2026-63942?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-63942?
Apply the vendor's patch.
Is CVE-2026-63942 being exploited?
There is no known exploitation of CVE-2026-63942 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-63942, DEBIAN-CVE-2026-63942, GHSA-g8r4-rq83-8vj2, ROOT-OS-UBUNTU-2204-CVE-2026-63942, UBUNTU-CVE-2026-63942.